This invention relates to cross-flow reactors or adsorbers where a fluid flows across a moving bed of catalyst or adsorbent. In particular, this relates to the internal components for distribution flow of the fluid and for providing a device for preventing the flow of catalyst or adsorbent across the inlet or outlet screens.
A wide variety of processes use radial flow reactors to provide for contact between a fluid and a solid. The solid usually comprises a catalytic material on which the fluid reacts to form a product. The processes cover a range of processes, including hydrocarbon conversion, gas treatment, and adsorption for separation.
Radial flow reactors are constructed such that the reactor has an annular structure and that there are annular distribution and collection devices. The devices for distribution and collection incorporate some type of screened surface. The screened surface is for holding catalyst beds in place and for aiding in the distribution of pressure over the surface of the reactor to facilitate radial flow through the reactor bed. The screen can be a mesh, either wire or other material, or a punched plate. For a moving bed, the screen or mesh provides a barrier to prevent the loss of solid catalyst particles while allowing fluid to flow through the bed. Solid catalyst particles are added at the top, and flow through the apparatus and removed at the bottom, while passing through a screened-in enclosure that permits the flow of fluid over the catalyst. The screen is preferably constructed of a non-reactive material, but in reality the screen often undergoes some reaction through corrosion, and over time problems arise from the corroded screen or mesh.
One type of inlet distribution device is a reactor internal having a scallop shape and is described in U.S. Pat. No. 6,224,838 and U.S. Pat. No. 5,366,704. The scallop shape and design provides for good distribution of gas for the inlet of a radial flow reactor, but uses screens or meshes to prevent the passage of solids. The scallop shape is convenient because it allows for easy placement in a reactor without concern regarding the curvature of the vessel wall. The screens or meshes used to hold the catalyst particles within a bed are sized to have apertures sufficiently small that the particles cannot pass through. A current optimizer, Optimiser™, design by United States Filter Corp., PCT application no. WO 01/66239 A2, has an improved shape, but still uses a screen comprised of wires having a sufficiently narrow spacing to prevent the passage of catalyst. A significant problem is the corrosion of meshes or screens used to hold catalyst beds in place, or for the distribution of reactants through a reactor bed. Corrosion can plug apertures to a screen or mesh, creating dead volumes where fluid does not flow. Corrosion can also create larger apertures where the catalyst particles can then flow out of the catalyst bed with the fluid and be lost to the process increasing costs. Catalyst containment loss can be due to mechanical failure of profile wire screens due to either component differential thermal growth or thermally cyclic operating environment. Differential thermal growth can cause bending of the profile wires creating a fish-eye formation, and catalyst bed pressure dynamics can create problem areas in the profile wire screens. This produces unacceptable losses of catalyst, and increases costs because of the need to add additional makeup catalyst.
The design of reactors to overcome these limitations can save significantly on downtime for repairs and on the loss of catalyst, which is a significant portion of the cost of processing hydrocarbons.